Effects Of Dietary Glutamine And Nucleotides On Growth Performance, Activities Of Digestive Enzymes, Antioxidant Enzymes Activities And Gene Exressions Of Half-smooth Tongue Sole (Cynoglossus Semilaevis) Post Larvae

Half-smooth tongue sole (Cynoglossus semilaevis) is one of the most important marine flatfish species reared in China. Two growth trials were conducted to investigate the effects of dietary glutamine and dietary nucleotides on C. semilaevis post larvae. Four isonitrogenous and isolipidic experimental diets supplementing 0.0%,0.5%,1.0% and 2.0% glutamine (with dietary free glutamine estimated to be about 0.03%,0.46%,0.91% and 1,73%), together with 6 isonitrogenous and isolipidic experimental diets supplementing 0.000%,0.018%,0.036%,0.054%,0.072% and 0.090% nucleotides mixture (Sigma; IMP:AMP:GMP:UMP:CMP=1:1:1: 1:1) were formulated and fed 5 times a day to C. semilaevis post larvae (35days after hatching) for 30 days.1. Effects of dietary glutamine on growth performance, activities of digestive enzymes and IGF-1 mRNA expression of C. semilaevis post larvaeThe results indicated that, survival, body length, final body weight and specific growth rate (SGR) of post larvae fed the diets with 0.5%to 2.0% glutamine were significantly higher than those fed the 0.0% glutamine diet (P<0.05). Activities of amylase in both pancreatic and intestinal segments were increased with increasing dietary glutamine level. Post larvae fed the diet with 0.5% or 1.0% glutamine supplementation showed significantly higher activities of trypsin in intestinal segments than those in fish fed 0.0% and 2.0% glutatime diets (P<0.05), while specific activities of alkaline phosphatase (AKP) and leucine-aminopeptidase (LAP) in brush border membranes (BBM) increased significantly (P<0.05) with increasing dietary supplementation of glutamine. Quantitative Real-time PCR showed that IGF-1 mRNA expression in larval visceral mass was significantly up-regulated by dietary glutamine supplementation, and 2.0% supplementation group showed the highest IGF-1 expression, which was significantly higher than the control group (P< 0.05). In summary, dietary glutamine supplementation could significantly improve the survival and growth performance of larval C,semilaevis, enhance activities of digestive enzymes and up-regulated the expression of IGF-1. The optimal dietary free glutamine level based on SGR for C. semilaevis post larvae in the present study was estimated to be approximately 0.63% dry diet.2. Effects of dietary glutamine on antioxidant abilities and stress resistance of C. semilaevis post larvaeFish fed the diet supplemented with 2.0% glutamine showed significantly lower malondialdehyde (MDA) contents in larval whole body compared to the control group (P< 0.05). Activities of whole-body serum superoxide dismutase (SOD) and catalase (CAT) showed no significant difference among dietary treatments (P>0.05), whereas glutathione peroxidase (GPX) were significantly higher in post larvae fed the diet with 0.5% glutamine supplementation than those of 2.0% treatment (P<0.05). Transcript levels of SOD and GPX were significantly up regulated to the maximum (P<0.05), and then decreased as dietary glutamine supplementation increased to 2.0%, whereas expression of catalase (CAT) exhibited a reverse trend to them. Median lethal dissolved oxygen levels decreased significantly in fish fed the diet supplemented with 0.5% or 1.0% glutamine when compared to those fed 0.0% and 2.0% glutamine diets, while HSP70 expression was significantly stimulated in fish fedthe diet supplemented with 0.5% or 2.0% glutamine after hypoxia stress (P<0.05). In conclusion, dietary glutamine supplementation could modulate the activities and mRNA expression of critical antioxidant enzymes, decrease the MDA level in post larvae whole-body and improve the hypoxia stress resistance capacities of C. semilaevis post larvae.3. Effects of dietary nucleotides on growth performance and activities of digestive enzyme of C. semilaevis post larvae The results indicated that, as dietary nucleotides supplementation level increasing from 0.000% to 0.018%, survival increased significantly and then decreased significantly with further supplementation (P<0.05). Differrent nucleotides level in diets significantly influenced the growth performance of C.semilaevis post larvae. Post larvae fed diets with 0.018% -0.054% nucleotides supplementation showed significantly higher final body length, final body weight and SGR than the control group (P<0.05). As dietary nucleotides supplementation level increasing, activities of trypsin in pancreatic and intestinal segments and activities of amylase in intestinal segments increased significantly at first, after peaking at 0.036% supplementation level, then decreased (P<0.05). Activities of amylase in pancreatic segments were significantly higher in fish fed the diet supplemented with 0.036% and 0.054% nucleotides than the control group (P<0.05). Specific activities of AKP and LAP in BBM increased significantly (P<0.05) and then leveled off with increasing dietary supplementation of nucleotides with no significant difference among nucleotides supplemented groups. To sum up, dietary nucleotides supplementation could improve survival and growth performance and enhance activities of digestive enzymes of C.semilaevis post larvae. The optimal dietary nucleotides supplementation level based on SGR for C. semilaevis post larvae in the present study was about 0.018% dry diet.4. Effects of dietary nucleotides on activities of non-specific immune related enzymes, antioxidant abilitiy and stress resistance ability of C. semilaevis post larvaeThe results indicated that, MDA contents in larval whole-body were significantly lower in fish fed the diet with 0.018%,0.036% and 0.072% nucleotides supplementation than those in fish fed the diet supplemented with 0.000% or 0.090% nucleotides (P<0.05). Activities of SOD in fish fed the diet supplemented with 0.018% to 0.054% nucleotides were significantly increased when compared to the control group (P<0.05).0.018% group showed significantly higher activities of iNOS than those in 0.072% group (P<0.05). However, no significant difference was found between nucleotides levels and activities of LZM in larval whole-body (P> 0.05).0.018% treatment showed significantly higher SOD mRNA expression than other treatments (P<0.05). GPX mRNA expression in 0.018% and 0.036% group were significantly lower than those in other treatments (P<0.05), and 0.018%, 0.054%,0.072% and 0.090% groups showed significantly lower CAT mRNA expression than those in the control group(P<0.05). Post larvae fed the diet with 0.018% nucleotides supplementation had the lowest median lethal dissolved oxygen level when subjected to hypoxia stress, significantly lower than those in 0.000% and 0.090% treatments. Meanwhile, nucleotides supplementation at both high and low levels significantly stimulated HSP70 mRNA expression after hypoxia stress (P< 0.05). In conclusion, dietary nucleotides supplementation could improve activities of non-specific immune related enzymes, enhance the antioxidant abilities and anti-hypoxia strss abilities of C. semilaevis post larvae.